With the construction of the ultra high voltage transmission grid, transmission technology of bulk power and long distance has been widely applied in China. In order to solve the problem existed in improving the transmission ability of large capacity unit, the technology of series capacitor compensation (including controllable series capacitor compensation, TCSC) has been largely applied. Otherwise, HVDC Transmission technology has been utilized in regional transmission grids to solve the stability problem of the large transmission grid, and that will form an AC-DC mixed transmission mode. Because of the application of these two advanced technology in power transmission networks, subsynchronous resonance occurs as a new hazard that will do harm to the grid and impact the security of power plants proper operation. According to the problem of subsynchronous resonance, we can utilize the subsynchronous damping control or blocking filter to increase SSR severity, but the largest hazard of subsynchronous resonance is the critical damage it brings to the large capacity unit's shaft. Because the inherent frequency of the turbo-unit is similar with the resonant frequency of the transmission grid, the grid's subsynchronous resonance will cause torsional oscillation on the turbo-unit's shaft, if the resonance damping of the grid is not enough (or to be negative), the grid will occur divergent subsynchronous resonance, that will cause the torsional oscillations to be divergent too, and the shaft will be broken into parts. This kind of accident will also bring huge loss, no matter the personal injuries or the equipment damages, to the stability of the regional network.
At present, the turbo-unit of regional network that has the possibility to have subsynchronous resonance should be applied with torsional stress relay (TSR) and real-time system to monitor the torsional oscillation of the shaft. When the mechanical fatigue reaches the fixed value or the torsional oscillation is in divergence form, TSR will trip the unit from the network, to safeguard the normal operation of the units.
The generators in large capacity power plant are always the same type (e.g. 4×600 MW units 8×600 MW units), and the same type units have the same mode shapes, if the subsynchronous resonance was occurred in operation process, situation of different generators torsional oscillations will be the same. When the subsynchronous resonance occurs, if all the generators were equipped with TSR and all the shafts fatigue reached the predetermined levels, the trip output contacts will be provided simultaneously. To lose numerous high-capacity generators at the same time will do great harm to the regional transmission networks. The present invention proposes the coordinated control principle of TSR in different units. This invention also provides the method to optimize the output of TSR by coordinate master station, and reduces the impact of tripping the generator breaker on transmission networks.